What is Dengue fever?Dengue fever (pronounced Den-gay) is a viral infection caused by the female mosquito (Aedes aegypti and Aedes albopictus). Dengue fever occurs in tropical and sub-tropical regions and usually increases in the hot and humid months. Dengue fever is not a new disease. It was discovered several hundred years ago. In recent years, dengue fever has become a major international public health concern.

Dengue fever nicknamed "breakbone fever" because dengue patients usually express contorted movements due to intense joint and muscle pain. Benjamin Rush from Philadelphia, US, first described "breakbone fever" in 1780. Slaves who developed dengue fever in the West Indies were said to have "dandy fever" because of their posture and gait.

Dengue fever lasts for approximately 7 days, despite its sudden and acute onset. However, extra precautions should be taken after the recovery period. These precautions will help prevent severe illness from occurring in some people, such as dengue haemorrhagic fever (DHF) or dengue shock syndrome (DSS). These illnesses are potentially lethal and are today the leading cause of childhood mortality in several Asian countries.

Aedes Mosquito

How is Dengue fever transmitted?
Dengue viruses are transmitted to humans (host) through the bites of the female striped Aedes aegypti mosquito (vector). This variety of mosquito breeds easily during the rainy seasons but can flourish in peridomestic fresh water, e.g. water that is stored in plastic bags, cans, flowerpots and old tires. The dengue virus is transmitted to its host during probing and blood feeding. The mosquito may carry the virus from one host to another host and the mosquito is most active in the early morning and later afternoon. A mosquito bite can cause the disease. Incubation period occurs when the viruses has been transmitted to the human host. The period ranges from 3 to 15 days (usually lasting for 5-8 days) before the characteristics of dengue appear. During incubation time, the dengue viruses multiply.

What are the characteristics of Dengue fever?
The Dengue virus travels to various glands in the body where it multiples. It then travels to the bloodstream, affecting some changes to these blood vessels. The virus may cause the blood vessels to swell and leak. The spleen and lymph nodes may also become swollen. Patches of liver tissue may die. Furthermore, a process known as disseminated intravascular coagulation (DIC) occurs. During this process, chemicals used to clot blood are used up, and thus severe bleeding (hemorrhage) occurs internally as well as the skin.

Basically, dengue commences with high fever and other signs as listed above for 2 to 4 days. Then, the temperature drops rapidly and intense sweating takes place. After about a day with normal temperature and a feeling of well-being, the temperature rises abruptly again. Rashes (small red bumps) show up on the arms, legs and the entire body simultaneously along with fever. However, rashes rarely occur on the face. The palms of the hands and soles of the feet may be swollen and bright red. Although the patient may feel exhausted for several weeks, most cases of dengue take approximately one week to recover. Once a person recovers from dengue, he or she will have antibodies in their bloodstream which will prevent them from having a relapse for about a year.

Treatment
There is no specific treatment to shorten the course of dengue fever. Medications are given to alleviate the signs and symptoms. Aspirin should not be given to patients. It will cause severe bleeding. Hence, it is advisable to take paracetamol to relieve muscle and joint aches, fever and headache. The patient may be required to be sponged down with water at room temperature using a wet, squeezed out towel for about 20 minutes at a time. This will help to help lower the high temperature. Ice water should not be used for this purpose. However, bed rest is essential to a speedy recovery and the patient should consume plenty of water which will help to alleviate the illness. Patients should be kept in a room that has screens to prevent mosquitoes from entering or else under mosquito netting until the second period of fever has subsided. Hence, mosquitoes cannot bite them. If the patient is bitten then the dengue virus may be transmitted to the mosquito and then to another host.

What is Dengue Hemorrhagic Fever (DHF)?
Dengue hemorrhagic fever occurs when the dengue virus re-infects a person who previously has experienced dengue fever. In this case, the previous infection teaches the immune system to recognize the virus, resulting in the immune system over reacting. DHF is also known as dengue shock syndrome (DSS) and the symptoms in this case are severe. It is a potential fatal immunological reaction and tends to affect children under 15 years old.

The initial symptoms of DHF are high fever and severe headache. Small purplish spots (petechiae) can be seen on the skin. This is because blood is leaking out of the vessels. Large bruised areas appear due to severe bleeding. Sometimes, patients may begin to vomit a substance that appears as coffee grounds. This is actually a sign of bleeding in the stomach. The severe hemorrhage results in a decrease of blood in the body. The low blood flow will unable to maintain adequate supply of blood to meet the metabolic requests of the cells in the body. This state of low blood flow is the defined as Dengue shock syndrome (DSS).

Patients with DHF must be closely monitored for the first few days until their condition is stabilized. The patient's condition may suddenly worsen after few days if the fever has not subsided. The temperature will then suddenly drop and the patient shows signs of circulatory failure. The patient may rapidly go into a critical state of shock (DSS) and die within 12 to 24 hours. However, he or she may recover quickly after appropriate volume replacement therapy. Fluids are infused to patients to avoid dehydration. Sometimes, blood transfusions may be necessary if severe bleeding occurs. In addition, oxygen is given to cyanotic (bluish) patients.

Prevention and ControlAt present, the only method of preventing and controlling dengue fever is to eradicate the mosquito population. They are a number of ways to combat the vector mosquitoes:

- Eliminate any sources that may collect water such as tins, bottles, plastic food containers and old tires. Mosquitoes breed easily in any source of standing water.

- Appropriate insecticides, such as larvicide's can be added to water containers and man-made ponds. The insecticides can prevent mosquitoes breeding for several weeks. However, they must be re-applied as per directions.

- Always clean and check drains to ensure they are not blocked especially during the rainy season.

- Breed small mosquito-eating fishes in an artificial pond to eradicate the mosquito larvae.

In addition to the above, there are a number of factors to help prevent the mosquito being attracted to human prey.

- Avoid wearing dark and tight clothing because mosquitoes are attracted to dark colours. Wear loose, white and long clothes, which cover the whole body. Mosquitoes find it difficult to bite through loose clothes than tight fitting clothes.

- Environmental conditions. It is suggested to sleep under mosquito netting or in a room which has mosquito screens on the windows. Mosquitoes are unlikely to bite in an air-conditioned room and under strong fans. Mosquito coils are also useful to help prevent mosquitoes from entering the room.

- Apply mosquito repellants.

- Avoid reduce outdoor activities during morning and late afternoon because Aedes mosquitoes are daytime feeders.